US Bridges

Nh 31 over Stony Brook

Poor

Hillsborough County, New Hampshire · 0.1 MI FM Lyndeborough Tl · Structure no. 027700940016200

Built
1929
96 years old, rebuilt 1983
Condition
Poor
inspected November 2024
Type
Frame
Concrete
Length
23 ft
1 main span
Daily traffic
3,496
2023 count
Owner
State
State Highway Agency

About this bridge

Nh 31 over Stony Brook is a concrete frame carrying Nh 31 over Stony Brook in Hillsborough County, New Hampshire. It was built in 1929 and reconstructed in 1983, so it is 96 years old, older than the New Hampshire average of 56.9 years.

The most recent inspection reported to the Federal Highway Administration rates it in poor condition with a lowest component rating of 4 out of 9. The lowest-rated primary component is rated 4 or below, indicating advanced deterioration. Poor does not mean unsafe; such bridges are inspected more often and may carry load restrictions.

It carries about 3,496 vehicles a day, roughly 4% of them trucks, projected to reach 5,174 by 2043. The structure is 23 ft (7 m) long and 36 ft wide. If it were closed, the detour would be 8.1 mi (13 km).

Location

Open in Google Maps
CarriesNh 31
CrossesStony Brook
Location0.1 MI FM Lyndeborough Tl
RouteState Highway 31
CountyHillsborough County
StateNew Hampshire
Coordinates42.86809, -71.77454
Functional classRural Major Collector

Condition and inspection

Poor

The lowest-rated primary component is rated 4 or below, indicating advanced deterioration. Poor does not mean unsafe; such bridges are inspected more often and may carry load restrictions.

ComponentRatingMeaning
Deck4 PoorAdvanced section loss, deterioration, spalling or scour.
Superstructure4 PoorAdvanced section loss, deterioration, spalling or scour.
Substructure7 GoodSome minor problems.
Channel and channel protection7 GoodSome minor problems.
Last inspectionNovember 2024
Inspection intervalevery 8 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation4: Meets minimum tolerable limits to be left in place as is
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating68 US tons
Inventory rating43.2 US tons

Structure

Structure typeFrame
MaterialConcrete
DeckConcrete, cast-in-place
Main spans1
Design loadH 15
Structure length23 ft (7 m)
Longest span20 ft (6.1 m)
Deck width36 ft (11 m)
Roadway width32 ft (9.8 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic3,496 (2023)
Projected traffic5,174 by 2043
Trucks4%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed8.1 mi (13 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerState Highway Agency
Maintained byState Highway Agency
Historic statusPossibly eligible for the National Register; requires further investigation
Work proposedReplacement because of substandard load-carrying capacity or roadway geometry
Estimated improvement cost$314,000 (2025 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was Nh 31 over Stony Brook built?

It was built in 1929, making it 96 years old in 2025. It was reconstructed in 1983.

What condition is Nh 31 over Stony Brook in?

The National Bridge Inventory rates it in poor condition. The lowest-rated primary component is rated 4 or below, indicating advanced deterioration. Poor does not mean unsafe; such bridges are inspected more often and may carry load restrictions. The last reported inspection was in November 2024.

How much traffic does Nh 31 over Stony Brook carry?

About 3,496 vehicles per day (2023 count), of which roughly 4% are trucks.

How long is Nh 31 over Stony Brook?

The structure is 23 ft (7 m) long with a longest span of 20 ft (6.1 m) and a deck 36 ft wide.

Who owns Nh 31 over Stony Brook?

It is owned by the State Highway Agency.